The angle structural shape generally comprises a pair of flanges lying substantially at a right angle to one another and formed with a radius or fillet along the interior of the vertex which is defined by the planar backs of the flanges or legs which adjoin at a sharp right angle.
The flanges may be of the same widths (equal widths) or of different widths, depending upon the use to which the angle iron or profile is to be put. Similarly the width of the flanges (lengths of the flange cross section) and the thickness of the flanges may be selected to suit the loading characteristics of the structural shape.
In the following description, reference may also be made to structural shape as a "profile", a term which has increasingly gained acceptance in the art.
Angle structural shapes of the type described above are basic elements in construction, forming corner members, connecting members, vertical and horizontal supports, can be welded or assembled with other angle profiles to produce more complex shapes and, generally, have wide application in all phases of the construction industry.
From the late 19th century through the turn of the century, and even to date, relatively complicated multipass rolling techniques have been used to produce these structural shapes. Indeed the basic descriptions of the processes date from 1875 and 1881 and involve seven and nine step rolling methods starting with a rectangular bar, for producing angle structural shapes. For the most part these techniques are effective only for producing angle shapes with equal flange widths and are relatively complicated, requiring a large number of pairs of rollers for the large number of passes which are involved.
In general these earlier techniques can be described as initially transforming a body of generally rectangular section into a blank having a central ridge angular cross section (triangular profile) which is maintained or sharpened in subsequent operations which progressively define the "wings" flanking the ridge. After six or eight passes, most of which result in a reduction of thickness of the wings, the latter are bent in the final rolling pass at right angles to one another to form the angle structural shape. These techniques are described subsequently with reference to the drawings.
Naturally, when a large number of passes are required to produce the angle shape, the number of man hours required for the setup of the mill for particular dimensions of these structural shapes is considerable, the equipment involved is complex and the output may be limited, all in spite of the relative simplicity of the angle structural shape.